Reference beacon methods and apparatus for TDOA/FDOA geolocation

Abstract

A method and apparatus for estimating bias errors in a time-difference-of-arrival/frequency-difference-of-arrival (TDOA/FDOA) geolocation system using a reference signal transmitter in which position and/or motion information of the reference signal transmitter is encoded into the reference signal. The motion information may include the velocity and/or acceleration of the reference signal transmitter. The reference signal is received by multiple collection platforms operating in conjunction with a geolocation system and a reference correction processing system. The reference correction processing system receives, via the multiple collection platforms, the position and/or motion information, which is immediately and unambiguously associated with specific reference signal transmissions. The geolocation system estimates the position and/or velocity of the reference signal transmitter using conventional TDOA/FDOA techniques. The estimated position and/or velocity of the reference signal transmitter is compared to the information contained in the reference signal to estimate bias errors.

1. A method of determining bias error in a geolocation system, comprising:
 transmitting from a transmitter a reference beacon signal containing transmitter position information and transmitter motion information, wherein the transmitter motion information includes at least one of a velocity and an acceleration of the transmitter; 
 receiving the reference beacon signal at a plurality of collection platforms; 
 measuring a time of arrival of the reference beacon signal at each of the plurality of collection platforms; 
 determining an expected difference between the times of arrival of the reference beacon signal at two of the plurality of collection platforms based on the transmitter position information contained in the reference beacon signal; 
 determining a timing bias error based on the measured times of arrival of the reference beacon signal at the two collection platforms and the expected difference between the times of arrival of the reference beacon signal at the two collection platforms; 
 measuring a frequency of arrival of the reference beacon signal at each of the plurality of collection platforms; 
 determining an expected frequency difference of arrival of the reference beacon signal at the plurality of collection platforms based on the transmitter motion information contained in the reference beacon signal; and 
 determining a frequency bias error based on the measured frequency of arrival of the reference beacon signal at each of the plurality of collection platforms and the expected frequency difference of arrival of the reference beacon signal at the plurality of collection platforms. 
 
   
   
     2. The method of  claim 1 , wherein the transmitter position information includes an estimate of a position of the transmitter at a time of transmission of the reference beacon signal. 
   
   
     3. The method of  claim 1 , wherein the transmitter position information includes a position of the transmitter at a time of fix and the reference beacon signal further contains the time of fix. 
   
   
     4. The method of  claim 1 , wherein the reference beacon signal contains information identifying the transmitter. 
   
   
     5. The method of  claim 1 , wherein the reference beacon signal contains error correction information. 
   
   
     6. The method of  claim 1 , wherein the position information is contained in an information element encoded in the reference beacon signal. 
   
   
     7. The method of  claim 6 , wherein the information element is transmitted two or more times. 
   
   
     8. The method of  claim 7 , wherein a pseudo-random waveform is transmitted between the transmissions of the information element. 
   
   
     9. The method of  claim 1 , wherein the timing bias error includes a position measurement error. 
   
   
     10. The method of  claim 1 , wherein the frequency bias error includes a velocity measurement error. 
   
   
     11. The method of  claim 1 , wherein the timing bias error is a differential timing bias error. 
   
   
     12. The method of  claim 1 , wherein the frequency bias error is a differential frequency bias error. 
   
   
     13. The method of  claim 1 , wherein the transmitter motion information includes an estimate of a motion of the transmitter at a time of transmission of the reference beacon signal. 
   
   
     14. The method of  claim 1 , wherein the transmitter motion information includes a motion of the transmitter at a time of fix and the reference beacon signal further contains the time of fix. 
   
   
     15. The method of  claim 1 , wherein the motion information is contained in an information element encoded in the reference beacon signal. 
   
   
     16. The method of  claim 15 , wherein the information element is transmitted two or more times. 
   
   
     17. The method of  claim 1 , wherein the transmitter position can vary with time.